The present invention relates in general to laser technology for treatment of transparent materials and more specifically to a method and apparatus for creating an image inside a transparent material, using a pulsed laser beam.
Some methods and apparatus were previously known for creating a variety of images inside and on the surface of a transparent material, using a pulsed laser radiation emitted by a solid-state laser.
One of such methods of image creation in a transparent material of the Plexiglas type is disclosed in U.S. Pat. No. 4,092,518 of May 30, 1978, Int. Cl. B23K27/00 or Nat.Cl. 219/121.
The method is as follows: a cylindrical article made of a transparent material is placed with its flat edge towards the laser beam and the laser radiation having a pulse duration in the range of 100 to 300 microseconds is focused inside the article using an optical lens.
The effect of the laser pulse creates a number of three-dimensional macrodestructions appearing as fanned out cracks.
A variety of such macrodestructions are produced in the article of a transparent material by changing the depth of laser beam focusing along the length of the article. The macrodestructions are shaped predominantly as saucers-like cracks of different size arranged randomly around the focal point thus establishing an optical decorative effect inside the transparent material.
Such a decorative effect is appreciably intensified when the said article is illuminated.
Used as a device for practical realization of said method is a multimode solid-state free-running pulsed laser and a convergent lens having a focal length from 100 to 200 mm for focusing laser radiation. Cylindrical articles of a transparent material having a diameter of 35 to 80 mm and a length of 85 to 205 mm are recommended for laser treatment.
The said technology enables three-dimensional but uncontrolled and abstractly shaped images to be obtained, which produce a decorative effect.
Moreover, the said technology fails to reproduce any desired image, accounting an uncontrolled behavior of macrodestructions occurring in the material being laser-treated.
Another known method of creating a pre-set image (e.g. image being copied by an optical camera) on the surface of a transparent material by a laser beam is disclosed in U.S. Pat. No. 4,843,207 issued on Jun. 27, 1989, IPC B23k26/00 or NPC 219/121. That patent discloses a method and a device for producing, by a laser beam, a decorative ornament on products made of a transparent material and having a hollow axially symmetrical cap-like shape.
The method comprises preconditioning of a product made of a transparent material, including forming a coating on the blank outer surface, being at least 1.2 mm thick and made of material featuring over 75% absorption of laser radiation at its operating wavelength.
Said coating may be formed either by a layer of colored glass or by a layer of precious metal.
A laser beam having a wavelength of 0.5 to 2.0 micrometers acts upon the external absorbing coating of the hollow product through the thick internal wall, thus causing a phase change on the external surface. The laser beam and the product treated by the beam mutually move so that the laser beam is focused on the surface.
To carry out the said method a device is used comprising a solid-state pulsed laser featuring an acoustooptic Q-switch, an optical lens and a mirror, both being movable along the axis of symmetry of the hollow product in such a manner that laser radiation is focused on the product's external surface being treated, while the mirror is capable of rotating.
All the motions mentioned above are controlled and monitored by a microcomputer and an optical camera which copies the pattern of a decorative ornament reproduced by the laser beam on the external surface of the product.
The discussed above known technology when applied for artistic treatment of glass makes it possible to impart adequately high decorative properties thereto.
However, such technology imposes some restrictions, that is, the product must be hollow and the maximum thickness of its wall is about 40 mm; a product made of a transparent material must be preconditioned on its external surface; the image being reproduced can be made only on the surface of the article.